The present invention relates generally to testing and more specifically to testing a dual mode interface, such as a bilingual 1394 firewire port.
Firewire, also known as IEEE 1394, is a personal computer and digital audio/video serial bus interface standard for high speed communications. Firewire currently supports data transfer rates up to 400 Mbps (in 1394a) and 800 Mbps (in 1394b), and the maximum data transfer rate possible with firewire 1394b is 1600 Mbps and likely to increase to 3200 Mbps. A single firewire port can typically be used to connect up to 63 external devices. In addition to its high speed, firewire also supports isochronous data—delivering data at a guaranteed rate. This makes firewire ideal for devices that need to transfer high levels of data in real-time, such as video devices.
A dual mode, or bilingual, 1394 firewire port (also referred to below as a bilingual firewire port) can operate in two different modes corresponding to the two different data rates described above. Specifically, a bilingual firewire port can operate at both speeds—1394a and 1394b—depending on the application. When the bilingual firewire port operates at the slower data transfer rates of 100, 200, or 400 Mbps, the bilingual firewire port operates in a “legacy mode”. When the bilingual firewire port operates at the higher data transfer rate of 800 Mbps, the bilingual firewire port operates in a “beta mode”. There is typically a method to set the bilingual firewire port to a particular mode, such as by causing a particular pin of the firewire port to have a voltage greater than a predetermined value for one mode and less than the predetermined value for the other mode. The voltage is set by control logic or an external signal.
One problem is that it is difficult to test the firewire port at its normal beta mode operating speed(s). Automated test equipment used in a non-invasive fashion (i.e., testing the firewire port using an external device not inserted onto the firewire port circuit itself) cannot normally communicate at the fast data rates of a beta mode firewire port. Further, the interface between the test equipment and the firewire port can introduce parasitic loading on the high-speed firewire port, thereby degrading performance. Therefore, firewire ports are traditionally tested using automated test equipment that communicates at a lower data rate relative to the firewire's beta mode operating data rates to determine that the firewire port is functional. This testing, however, does not test the firewire port for proper operation at the maximum data rates.
Another method of testing a bilingual firewire port is in an invasive fashion in which test circuitry is inserted onto the circuit board of the firewire port itself during manufacturing testing of the firewire port. For example, test circuitry may be inserted on input/output data lines of the firewire port to analyze the data being transmitted/received by the firewire port. This technique, however, is undesirable because it adds parasitic loading on the firewire port and can alter the operation of the components.
Therefore, there remains a need to enable testing of a bilingual firewire port at the maximum speed which the bilingual firewire port operates and in a non-invasive fashion.